This application claims the benefit of German patent application 101 04 423.2 filed Feb. 1, 2001, herein incorporated by reference.
The present invention relates generally to a godet roll for guiding at least one yarn and, more particularly, to a godet roll comprising a projecting support on which a hollow-cylindrical godet roll casing forming a circumferential yarn guiding surface is rotatably supported by a plurality of bearings, at least one of the bearings comprising a radially acting magnetic bearing having a plurality of bearing pole windings spaced circumferentially relative to the godet roll casing.
A godet roll of the above-described type to which the invention relates is disclosed in European Patent Publication EP 0 770 719 B1. This known godet roll has a godet casing connected with a motor and seated on a support. Two magnetic bearings arranged at a spacing from one other are provided for seating the godet casing, each of the magnetic bearings having several bearing pole windings. In this godet roll, the bearing pole windings of the magnetic bearing are arranged on the support in a common bearing plane oriented such that the direction of the radial forces exerted by the bearing pole windings act in the bearing plane perpendicularly in respect to the axis of rotation of the godet roll. The bearing pole windings face the interior circumference of the godet roll casing, or the exterior circumference of a driveshaft supporting the godet roll casing from two orthogonal directions.
This arrangement of the magnetic bearings is intended to make it possible to employ the godet roll for yarn treatment at high speeds, e.g., at speeds up to 8,000 meters per minute (m/min.). However, problems may be experienced because the godet rolls, which are seated in two bearing planes and rotate at high speed, must have a comparatively high rigidity to prevent deformations of the godet roll between the bearing planes and outside of the bearing planes. Special particular shapes, materials and material strengths are required to obtain sufficient rigidity. As a result, the godet roll has a large mass and requires correspondingly large, spatially extensive bearings, whereby sympathetic vibrations can occur at low natural frequencies. Such sympathetic vibrations at low natural frequencies in turn can lead to deformations and, in an extreme case, to the destruction of the godet roll. The need for definite rigidity, along with the danger of sympathetic vibrations, are obstacles to the operation of the godet roll at high speeds. A further disadvantage of the known godet roll is that the magnetic bearings with their bearing pole windings can only be used with a correspondingly large exterior diameter of the godet roll casing, in particular since the stress on the godet roll caused by the yarn guide requires a minimum pole size of the bearing pole windings.
It is therefore a basic object of the present invention to provide an improved godet roll of the type described above, and more specifically, to provide a godet roll in which the danger of deformations because of sympathetic vibrations is reduced and large bearing stresses can be assuredly absorbed even with godet roll casings of small diameter.
In accordance with the present invention, these objects are addressed by providing a godet roll wherein the bearing arrangement for the godet roll casing comprises a radially acting magnetic bearing having a plurality of bearing pole windings spaced about the support in the circumferential direction relative to the godet roll casing and also spaced along the support in a plurality of adjacent bearing planes. Thus, the present godet roll is distinguished in that the godet roll casing is radially supported over a larger bearing area extending in the longitudinal direction of the godet roll casing. In this manner, a sufficient rigidity is created, even with thin-walled godet casings, which makes it possible to operate the godet roll at high speeds without vibration problems. By means of this arrangement of bearing pole windings in accordance with the present invention, it is possible to utilize the largest possible bearing pole windings into the installation space available within the godet roll casing, so that magnetic bearings with a great support strength in particular can be provided.
As used herein, a godet roll is intended and is to be understood to comprise any rotating roller employed for yarn guidance in textile machines or spinning installations. Therefore the present invention is intended to encompass both godet rolls whose godet roll casing is driven by a drive mechanism, for example an electric motor, or where the godet roll casing is seated freely rotatable in the support.
The distribution of the bearing pole windings over the support allows a uniform distribution of the positions of the bearing pole windings on the surface of an imagined cylinder arranged around the axis of rotation of the godet roll and extending through the bearing poles. In a godet roll of the prior art, the bearing poles of the magnetic bearing are arranged in a single bearing plane. Distributing the bearing pole windings over an additional bearing plane alone results in a considerably more uniform distribution of the position of the bearing pole windings on this imagined surface area, for example in godet rolls whose axial dimension is greater than their diameter.
An arrangement of the bearing pole windings in more than three bearing planes can make possible further uniformity in the positions of the bearing pole windings on the imagined surface area, in particular with godet rolls of a large axial dimension.
The arrangement in accordance with the present invention of the bearing pole windings via the support leads to an uniform distribution of the positions at which a force is introduced into the radial seating of the godet roll surface area. The tendency of the godet roll to become deformed at high speeds, for example to bend in case of sympathetic vibrations, is reduced. A reduced spacing between the bearing pole windings corresponds to a reduced free distance of the godet roll surface area to be bridged. In addition to the reduced deformability, the requirement for rigidity of the godet roll casing is also reduced. As a result, it is possible to utilize a godet roll casing of reduced mass, and therefore higher natural oscillations. A reduced tendency to deform and a reduced mass allow the operation of the godet roll at higher speeds.
In accordance with an advantageous further aspect of the present invention, at least some of the bearing pole windings can be arranged at offset angles from one bearing plane to another bearing plane. In case of such an angular offset arrangement of two bearing pole windings, the angular position of a second bearing pole winding in a second bearing plane is differentiated from a first bearing pole winding in a first bearing plane. The angular position of a bearing pole winding is the position of the bearing pole winding at the circumference of the support, or at the circumference of an imagined cylinder, in relation to a reference position expressed as the angle between the radius of the position and the radius of the reference position. If a position perpendicularly above the axis of rotation is selected as the reference position, the angular positions perpendicularly below the axis of rotation are 180 degrees spaced therefrom, and those of the lateral positions on the level of the axis of rotation are 90 degrees and 270 degrees spaced therefrom.
With an angularly offset arrangement of the bearing pole windings, the directions from which a force is exerted on the godet roll casing vary. This arrangement makes possible a radial seating of the godet roll casing with an arrangement of only one or two bearing pole windings in one bearing plane, and possibly also in a plurality of bearing planes. In the process, it is necessary that the bearing pole windings of different bearing planes cooperate. The distribution of the bearing pole windings over the stator can be made further uniform by means of an angularly offset arrangement of the bearing pole windings from bearing plane to bearing plane.
In accordance another aspect of the present invention, a spirally-extending arrangement of at least some bearing pole windings from one bearing plane to the next achieves further uniformity in the distribution of the bearing pole windings on the support. It is advantageous if the angular offset of the bearing pole windings from bearing plane to bearing plane lies between 90 degrees and 180 degrees, for example at 120 degrees, and the helix formed by the spiral arrangement of bearing pole windings extends over at least two revolutions.
An arrangement wherein the bearing pole windings individually arranged in the bearing planes increases the planar character of the radial seating of the godet roll casing, which can make possible further uniformity in the distribution of the bearing pole windings on the support.
The arrangement of the bearing pole windings in pairs opposite each other in the respective bearing planes can make possible an even distribution of the bearing pole windings over the support, in particular in connection with godet rolls of large diameter. This arrangement is particularly suited for achieving greater plane-related bearing forces.
However, for increasing the bearing force, there is also the possibility of arranging the bearing pole windings of adjacent bearing planes overlappingly in the circumferential direction of the support.
To assure that all bearing pole windings of the magnetic bearing work together, a sensor for monitoring a bearing gap is assigned to each one of the bearing pole windings in accordance with an advantageous further development of the invention. The sensors and the bearing pole windings are connected with a control device, so that every signal bearing gap deviation can be immediately corrected. This arrangement provides the option of controlling every bearing pole winding individually by means of the control device, or controlling as a pair two bearing pole windings located opposite each other in one or several bearing planes by means of the control device.
With longer godet rolls, the godet roll casing is preferably seated by means of two radially acting magnetic bearings, arranged at a distance from each other and additionally by an axial bearing for absorbing the axial forces. In order to achieve the greatest possible support of the godet roll casing by the magnetic bearing, the bearing pole windings of the magnetic bearings are arranged in at least three bearing planes. It is also possible to arrange the bearing pole windings of the one magnetic bearing, as well as bearing pole windings of the other magnetic bearing, in a common center bearing plane.
The axial bearing is preferably embodied as an axially acting magnetic bearing in order to obtain a contactless guidance, so that higher speeds of the godet roll are made possible.
At least one catch bearing may be provided, as a contactless radial bearing or a resiliently clamped radial bearing, which also makes possible higher speeds of the godet roll.
For seating the godet roll casing, the godet roll of the present invention is preferably designed with the support which receives the bearing pole windings embodied such that the bearing gap is formed between the pole ends and the godet roll casing, whereby the magnetic forces act directly on the godet roll casing.
However, there is also the option of embodying the support for receiving the bearing pole windings such that the bearing gap is formed between the pole ends and a shaft penetrating the support, wherein one end of the shaft is fixedly connected with the godet roll casing and the opposite end is coupled to a drive mechanism. Such an embodiment of the present invention has the advantage of making it possible to omit an additional seating in the drive mechanism, and in addition, the annular space formed between the godet roll casing and the support is available for receiving a heating arrangement. The godet roll casing can be heated by means of a heating arrangement placed on the circumference of the support in order to make it possible to perform a thermal treatment of the yarn.